The present invention relates to cutting tools and more particularly to finish reamers.
In a wide variety of manufacturing and repair or reconditioning processes, it is necessary to accurately cut a hole or bore to a predetermined inner diameter. For example, such a cutting operation is performed in some of the various methods which have heretofore been developed for rebuilding of internal combustion engine valve guides. After extensive use, the valve guides of an internal combustion engine will wear presenting excessive clearance between the valve guide and the valve stem. This excessive clearance may have an adverse effect on valve train operation and also increases undesirable emissions from the internal combustion engine.
The various methods heretofore proposed have included lining or relining of the worn valve guides with generally cylindrical inserts. In a typical rebuilding process, a worn valve guide is bored out to receive the insert which is press fit or forced into the bored out valve guide passageway. The insert is finish reamed so that the internal diameter is accurately cut and dimensioned with respect to the stem of the valve which reciprocates within the rebuilt valve guide.
Inserts of various materials, such as cast iron, thin wall, silicon bronze-aluminum and phosphor bronze, have been employed in such rebuilding methods. Cast iron inserts present certain inherent problems primarily related to cost, rate of wear and heat transfer characteristics. In order to overcome these problems, different forms of bronze, and particularly phosphor bronze, inserts have been developed. The phosphor bronze material is harder than cast iron and silicon bronze-aluminum. Phosphor bronze inserts provide increased wear characteristics and heat transfer properties. Examples of phosphor bronze inserts may be found in U.S. Pat. No. 3,828,415 entitled METHOD AND APPARATUS FOR REBUILDING VALVE GUIDES and issued on Aug. 13, 1974, to James A. Kammeraad and Donald J. Kammeraad and U.S. Pat. No. 4,103,662 entitled INSERT FOR REBUILDING VALVE GUIDES and issued on Aug. 1, 1978, to James A. Kammeraad.
One of the inserts disclosed in U.S. Pat. No. 3,828,415 is a thin wall tubular member stamped from a blank of phosphor bronze and progressively formed into a tubular shape leaving a longitudinal slit. The insert is forced into a reamed valve guide by means of an adapter. The outer diameter of the insert is greater than the reamed valve guide so that the insert is radially compressed when it is forced into the reamed valve guide. The insert is then trimmed so that it is flush with the valve guide. The inner surface of the insert may then be knurled to flow the metal and seal off the passage through the slit. Finally, the valve guide is finish reamed to a predetermined diameter as required for the particular size of valve stem. The tubular insert has a wall thickness in the range of 10 to 25 thousandths of an inch and is preferably in the range of 15 to 20 thousandths of an inch.
An insert as disclosed in U.S. Pat. No. 4,103,662 includes an inner sleeve or tube of spring-tempered phosphor bronze and an outer carrier sleeve or tube of steel or aluminum. The separate formation of the inner and outer sleeves allows precise control of wall thicknesses, diameters and concentricities.
With each type of valve insert disclosed in the aforementioned patents, the finish reaming step is typically, although not always, performed with a high speed reamer. Reamers are fabricated in a plurality of graduated, standard diameter sizes to accommodate the different sizes of valve guides. The reamers each include a plurality of flutes which define cutting blades. The flutes may be straight or spiral cut. Typically, a spiral flute reamer is used since it provides a better finish and a smoother cutting of the insert passageway than a straight cut reamer.
Conventional reamer blades each include a rake face, a cutting edge, a land having a margin and a relief, and a trailing portion. The land may be circular or convex and is typically relieved to avoid interference and rubbing with the work piece. Such reamers may be manufactured from high speed steel and a fluting cutter is employed to cut the flutes into the reamer blank. Further, the reamer portion may be back tapered to prevent binding of the reamer within the bore which is being enlarged and finished. An example of a prior reamer may be found in U.S. Pat. No. 2,940,342 entitled REAMERS and issued on June 14, 1969, to Lavallee.
The heretofore available finish reamers employed to finish the passageways of phosphor bronze valve inserts have suffered from various problems primarily related to wearability. The prior reamers after five or six reaming operations are no longer able to hold their size. Use of the tool for additional reaming operations results in unacceptable dimensioning and finishing of the phosphor bronze valve guide insert.